ABSTRACT
This chapter discusses the domain of magnetohydrodynamics. Ultra-low-frequency waves can, in appropriate circumstances, interact with energetic particles. In such circumstances, it may be necessary to use the ideas of kinetic theory in order to treat the problem. The chapter considers the effect of non-thermal particle distributions leading to micro-instability. The fact that the wave was damped, rather than amplified, arose because of the bi-Maxwellian form that we assumed for the zero-order distribution function. The chapter outlines some general principles, independent of the precise nature of the zero-order distribution function, which will provide a basis for studying specific cases when the nature of the distribution function is known. The nature of the wave-particle interaction found from the perturbed distribution function depends on the model adopted for the zero-order distribution function. In a collisionless medium, a population of energetic particles with an unstable distribution function can lead to wave growth of MHD waves through interaction with the parallel electric field.
